1. Field of Invention
The present invention relates in general to the electrical connector field. More particularly, the present invention relates to land grid array (LGA) connectors incorporating a frame structure having one or more power distribution elements (e.g., bus bars).
2. Background Art
Electrical connectors are in widespread use in the electronics industry. In many computer and other electronic circuit structures, an electronic module such as a central processor unit (CPU), memory module, application-specific integrated circuit (ASIC) or other integrated circuit, must be connected to a printed wiring board (PWB). Printed wiring boards are also known as printed circuit boards (PCBs) and etched wiring boards. When populated with one or more electronic components, a printed wiring board is often referred to as a printed wiring board assembly (PWBA) or a printed circuit board assembly (PCBA). In connecting an electronic module to a PWB, a plurality of individual electrical contacts on the base of the electronic module must be connected to a plurality of corresponding individual electrical contacts on the PWB. This set of contacts on the PWB dedicated to contacting the electronic module contacts is known as a land grid array (LGA) site when a LGA connector is used to connect the electronic module to the PWB.
Rather than permanently soldering the electronic module contacts to the LGA site, it is desirable to use LGA connectors that allow the electronic module to be installed to and removed from the LGA site. LGA connectors provide the user with the flexibility to upgrade or replace electronic modules during the manufacturing cycle and in the field. LGA connectors are also known as sockets, interconnects, interposers, carriers, and button board assemblies. Generally, LGA connectors include “true” LGA connectors where both the PWB and the electronic module are mated with contacts through mechanical/pressure contact, as well as “hybrid” LGA connectors where the contacts are soldered to the PWB and make mechanical/pressure contact with the electronic module.
In general, LGA connectors provide electrical connections between two parallel electrical substrates in computing equipment through the use of an interposer. Typically, one of these substrates is a PWB and the other is an electronic module, which may, for example, have either a ceramic or organic laminate substrate. However, supplying power or current into the LGA connectors can create design difficulties and usage limitations.
PWBs typically include multiple conductive layers laminated with insulating plastic therebetween. The conductive layers are typically reserved for power, power return, ground, and signals. The layers reserved for signals are typically etched to form “traces” that conduct the signals. The layers reserved for power, power return and ground are typically referred to as “power planes”, “power return planes”, and “ground planes”. The reason these layers are referred to as planes is because they typically extend in a planar region to distribute power over at least a portion of the PWB. Various of the conductive layers may be connected together through drilling holes called vias and then plating each via with a conductor to form a plated-through-hole (PTH). Typically, the planes are interrupted by clearance holes to avoid shorting to the plated-through-holes. These clearance holes, as discussed in more detail below, can make power distribution difficult in certain portions of the PWB, including the LGA site, because in those portions the planes may resemble something akin to “swiss cheese” due to a high concentration of clearance holes.
Since typical electronic modules use multiple voltages for various chips and functions, the planes in the PWB that are reserved for power are typically divided into multiple domains. As the LGA contacts are assigned to various functions, the PTH of the PWB associated with a particular LGA contact has to be isolated from other planes by clearance holes in the plane or anti-pad to prevent electrical shorts. These clearance holes may, for example, account for greater than approximately ⅔ of the PTHs on a given power plane. Typically, each clearance hole is about ¾ of the width of the LGA contact pitch. Thus, over ½ of the power plane can be missing in any row or column of LGA contacts, which increases the power plane electrical resistance and power dissipation due to current flow.
A trend in the electronics industry has been to increase both the quantity of LGA sites and the density of each LGA site, i.e., the number of contacts per unit area at the LGA site. This trend exacerbates the power distribution problem that is associated with LGA connectors.
It should therefore be apparent that a need exists for an enhanced mechanism for power distribution in LGA connectors used to connect two substrates.